(1) Field of the Invention
The present invention relates to an electophotographic image-forming process and a magnetic developing sleeve for use in carrying out this process. More particularly, the present invention relates to an improvement in the process for forming a sharp image having reduced fogging from a mixture of a photosensitive toner and a magnetic carrier.
(2) Description of the Related Art
The image-forming process using a photosensitive toner has been known from old, and there has already been proposed a process in which an image is formed by simultaneously performing light exposure and image transfer with application of voltage. For example, Japanese Unexamined Patent Publication No. 60-98463 and Japanese Unexamined Patent Publication No. 60-138566 disclose a process in which a photosensitive toner layer is formed on an electroconductive substrate, a transparent electrode is disposed to confront the toner layer, a bias voltage is applied so that the toner-applied side of the substrate has a polarity reverse to that of the toner and the counter electrode side of the substrate has the same polarity as that of the toner, imagewise light exposure is carried out, and the irradiated toner image is transferred to the counter electrode side.
However, in the above-mentioned simultaneous voltage application-light exposure-transfer process, charges of a polarity reverse to the polarity inherently possessed by the toner are injected in the photosensitive toner of the light exposure zone (bright zone), and this toner charged with the reverse polarity is electrostatically attracted to the counter electrode side to effect formation of an image. Accordingly, the image formed by the above-mentioned process is a negative image, and because of the principle of this image-forming process, it is impossible to form a positive image on the counter electrode side according to the above-mentioned process.
In Japanese Unexamined Patent Publication No. 01-137270, we have proposed an image-forming process in which two electrode surfaces, at least one of which has a curvature surface and at least one of which is transparent, are arranged to confront each other, a photosensitive layer is formed on one electrode surface, a bias voltage is applied so that the toner layer-supporting electrode surface has the same polarity as that of the toner charge and the counter electrode surface has a polarity reverse to that of the toner charge, the toner layer is irradiated with light at a position where both the electrode surfaces are brought into contact with each other through the photosensitive toner layer and the unexposed toner is transferred to the counter electrode side to effect formation of an image. It is taught that an electroconductive sleeve having a magnet disposed in the interior thereof is used as an electroconductive supporting electrode surface for the above-mentioned toner layer-supporting electrode surface and a photosensitive toner is used in the form of a magnetic brush of a mixture with a magnetic carrier for formation of an image.
This process proposed by us is advantageous in that a positive image can be formed by the simultaneous voltage application-light exposure-transfer process, and the above-mentioned magnetic brush performs simultaneously adhesion of the charged photosensitive toner and scraping of the light-exposed electricity-removed toner from the surface of the transparent electrode. However, scraping of the light-exposed electricity-removed toner from the surface of the transparent electrode is not sufficiently performed and therefore, a problem of fogging on the formed image arises.
More specifically, in the process for forming an image through the steps of supplying a mixture of a photosensitive toner and a magnetic carrier onto a developing sleeve having a magnet disposed in the interior thereof to form a magnetic brush of the mixture, bringing the magnetic brush into contact with an electroconductive substrate to form a photosensitive toner layer on the substrate, subjecting the photosensitive toner layer to imagewise light exposure to form a combination of the electricity-removed toner and the charged toner, and removing the electricity-removed toner from the electroconductive substrate by the contract with the magnetic brush, scraping of the electricity-removed toner from the electroconductive substrate is very important. Namely, only by removal of electricity or application of a bias voltage between the developing sleeve and the electrode surface, it is difficult to completely remove the photosensitive toner which has once adhered to the electroconductive substrate, and even by performing the sliding contact with the magnetic brush, complete removal of this photosensitive toner is impossible and fogging is caused to such a degree as degrading the sharpness of the image.